I don't think it's as simple as it sounds. I too have a 10x10 enlarger; however, mine has a 1000 watt head. At first glance one would think that a higher wattage head would decrease exposure times. However, a number of factors influence the intensity of light reaching the paper. First, light output decreases with distance. It's called the inverse square law. With my durst the bukb is about 2 feet from the negative. My old beseler 45 had the bulb a few inches from the negative. In addition, every enlarger head uses a different method to direct the light towards the paper. Furthermore, the light is being projected over a larger 10x10 area (100 sq in) instead of 5x5 (25 sq in).

In practice, I've noticed that my 10x10 durst usually requires a slightly longer exposure for the same negative.